The decision to build a second nuclear power station was made without public participation, Earthlife Africa Cape Town said on Tuesday.
Environmental and socio-economic assessments were also ignored, according to Maya Aberman, the organisation's campaign co-ordinator.
" can only assume that either the Minister isn't aware of the provisions of the Constitution and laws governing South Africa, that he considers these provisions irrelevant, or that he is attempting to inspire a false sense of optimism about his and his department's nuclear fantasies," Aberman wrote in a statement.
Earthlife Africa also claimed that the public enterprises department was busy finalising its national nuclear energy strategy, and was at work on a uranium mining and beneficiation strategy, without public input.
"Earthlife Africa Cape Town was under the impression that government strategies were formulated with some level of input from stakeholders and made at least an attempt to gather the opinions and concerns of affected citizens."
Public enterprises spokesperson Gaynor Kast could not be reached for comment.
Erwin told parliament on Monday that the government had approved the construction of a second nuclear power station in the southern part of the country. - Sapa